Re: [PATCH v8 4/5] docs: rpmsg: add virtio config space details

[Arnaud POULIQUEN <arnaud.pouliquen@foss.st.com>]

On 8/28/26 16:58, Tanmay Shah wrote:
> The virtio config space can provide single rpmsg buffer size in each
> direction. Document details of the configurable buffer size via virtio
> config space.
> 
> Signed-off-by: Tanmay Shah <tanmay.shah@amd.com>
> ---
> 
> Changes in v8:
>    - "%s/or differnt RX and TX sizes)/or different RX and TX queue sizes)/"
> 
> Changes in v6:
>    - rpmsg.rst: modify alignment related documentation
> 
> Changes in v5:
>    - fix documentation of buffer alignment
> 
>   Documentation/staging/rpmsg.rst | 17 +++++++++++++++++
>   1 file changed, 17 insertions(+)
> 
> diff --git a/Documentation/staging/rpmsg.rst b/Documentation/staging/rpmsg.rst
> index 63612b7ee120..d711d1643bab 100644
> --- a/Documentation/staging/rpmsg.rst
> +++ b/Documentation/staging/rpmsg.rst
> @@ -299,3 +299,20 @@ by the bus, and can then start sending messages to the remote service.
>   
>   The plan is also to add static creation of rpmsg channels via the virtio
>   config space, but it's not implemented yet.
> +
> +Configurable buffer sizes
> +=========================
> +
> +By default each rpmsg buffer is 512 bytes, and the same size is used for both
> +the receive and transmit directions. Remote processors that need a different
> +size (for example a larger MTU, or different RX and TX queue sizes) can
> +advertise it through the virtio device config space by setting the
> +VIRTIO_RPMSG_F_BUFSZ feature bit.
> +
> +When this feature is negotiated, the driver reads struct virtio_rpmsg_config
> +from the config space. This structure provides the size of a single buffer for
> +each direction (TX and RX). The device should advertise TX/RX buffer sizes
> +that already satisfy its own alignment constraints.

Nitpicking: following sentence seems to me more explicit as the alignment
concerns the buffer address. It is only a suggestion

The device should advertise TX/RX buffer sizes that already satisfy the
alignment constraints of its buffers.

Thanks,
Arnaud

> +
> +If the feature is not negotiated, the default 512-byte buffers are used for
> +both directions.